Method and device for removing decay heat from liquid metal reactors using thermosyphon

ABSTRACT

A method and device for removing decay heat from a liquid metal reactor using a thermosyphon so as to cool the reactor is disclosed. The method and device of this invention uses a thermosyphon heating part in place of a conventional air separator, thus improving its decay heat removal capacity. In the method of this invention, decay heat from the reactor is absorbed at the flowing air and additionally at the evaporator section of the thermosyphon. The absorbed heat at the evaporator section is, thereafter, dissipated to the atmosphere from the condenser section of the thermosyphon. In the liquid metal reactor installed at a position between a containment and a reactor support concrete wall, the thermosyphon is installed at a position between the concrete wall and the containment vessel. The thermosyphon has a vertical evaporator section, an inclined adiabatic section extending upward from the top end of the evaporator section, and a vertical condenser section extending upward from the top end of the adiabatic section. Using a thermosyphon also reduces the temperature of the exhaust air of the cooling channel.

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] The present invention relates to a method and device for removing passive decay heat from liquid metal reactors and, more particularly, to a method and device for effectively removing passive decay heat from liquid metal reactors using a thermosyphon heating part in place of a conventional air separator typically set in the heat transfer section of such a liquid metal reactor, thus improving its heat transfer capacity for transferring heat from a containment vessel, desirably reducing the temperature of exhaust air, and improving its decay heat removal capacity.

[0003] 2. Description of the Prior Art

[0004] A passive safety decay heat removal system (PSDRS) for liquid metal reactors has been actively and recently studied, developed and designed in the USA and Korea. In such a PSDRS, the cooling operation for cooling the hot sidewall of a containment vessel surrounding a reactor vessel is accomplished by a natural circulation of atmospheric air, with circulation force for the air passively generated by a difference in the density between hot air flowing in a hot air passage and heated by the hot sidewall of the containment vessel and atmospheric air flowing in a cold air passage outside the hot air passage. Since the conventional PSDRS for liquid metal reactors is designed to use such a passive safety decay heat removal technique, it has a high degree of operational reliability. Another advantage of the conventional PSDRS resides in that it effectively and naturally removes decay heat from a liquid metal reactor without requiring any separate power source or any operator's control.

[0005]FIG. 4 is a sectional view, showing the construction of the conventional PSDRS for liquid metal reactors recently studied in Korea. As shown in the drawing, this PSDRS is designed to dissipate decay heat from a liquid metal reactor to the atmosphere through a containment vessel 4 surrounding a reactor vessel 3. In a detailed description, a concrete wall 2 entirely surrounds the PSDRS, with an air separator 11 set in the channel between the concrete wall 2 and the containment vessel 4 and dividing the channel into a hot air passage and a cold air passage. In such a case, the hot air passage is defined between the containment vessel 4 and the air separator 11, while the cold air passage is defined between the concrete wall 2 and the air separator 11 as best seen in FIG. 5. Air inlet and outlet chimneys (not shown) are provided at the sidewall of the containment vessel 4. FIG. 7 is a view, showing a heat transfer mechanism of the conventional PSDRS having the air separator 11. As shown in this drawing, the heat transfer from the hot containment vessel 4 of the PSDRS to the air separator 11 is the radiant heat transfer (Rad). Meanwhile, the heat transfer from the hot containment vessel 4 of the PSDRS to air in the hot air passage is the first convective heat transfer (Conv1), and the heat transfer from the air separator 11 to the air in the hot air passage is the second convective heat transfer (Conv2).

SUMMARY OF THE INVENTION

[0006] Accordingly, the present invention is to provide a method and device for removing decay heat from liquid metal reactors, which uses the heating part of a thermosyphon or heat pipe in place of a conventional air separator, thus improving its decay heat removal capacity for liquid metal reactors.

[0007] Through this configuration, the air separator wall temperature (wall temperature of the thermosyphon heating part) is reduced and the heat dissipation from the hot wall, i.e. containment vessel 4 is increased. The increase is estimated to be 20%˜40%. This increase results in the overall heat transfer capacity of a decay heat removal device such as PSDRS. Also using a thermosyphon induces a reduction in the air temperature since the thermosyphon provides an additional path of heat transfer to the final heat sink, i.e. the environment air. The reduction in the air temperature introduces decrease of the temperature of the concrete wall 2 that is relatively weak to high temperature. The decrease helps the system in maintaining mechanical integrity for long term operation of a decay heat removal device such as PSDRS at a plant accident.

BRIEF DESCRIPTION OF THE DRAWINGS

[0008] The above and other objects, features and other advantages of the present invention will be more clearly understood from the following detailed description taken in conjunction with the accompanying drawings, in which:

[0009]FIG. 1 is a sectional view, showing the construction of a PSDRS using a thermosyphon in accordance with the preferred embodiment of the present invention;

[0010]FIG. 2 is a view, showing a heat transfer mechanism of the PSDRS using a thermosyphon heating part according to the present invention;

[0011]FIG. 3 is a plan view of the PSDRS using the thermosyphon according to the present invention, showing an arrangement of the parts of the PSDRS;

[0012]FIG. 4 is a sectional view, showing the construction of a conventional PSDRS having an air separator for KALIMERs currently developed by KAERI of Korea;

[0013]FIG. 5 is a view, showing a heat transfer mechanism of a conventional PSDRS using both an air separator and a separate radiation structure;

[0014]FIG. 6 is a view, showing the construction and operational theory of a conventional two-phase closed thermosyphon; and

[0015]FIG. 7 is a view, showing the heat transfer mechanism of the conventional PSDRS having an air separator.

DETAILED DESCRIPTION OF THE INVENTION

[0016]FIG. 1 is a sectional view, showing the construction of a PSDRS using a thermosyphon in accordance with the preferred embodiment of the present invention. FIG. 2 is a view, showing a heat transfer mechanism of the PSDRS using a thermosyphon heating part according to this invention. FIG. 3 is a plan view of the PSDRS using the thermosyphon according to this invention, showing an arrangement of the parts of the PSDRS. FIG. 4 is a sectional view, showing the construction of a PSDRS for KALIMERs. FIG. 5 is a view, showing a heat transfer mechanism of a conventional PSDRS using both an air separator and a separate radiation structure. FIG. 6 is a view, showing the construction and operational theory of a conventional two-phase closed thermosyphon. FIG. 7 is a view, showing the heat transfer mechanism of the conventional PSDRS having an air separator.

[0017] As shown in the drawings, the decay heat removal method of this invention comprises the steps of absorption of decay heat from the reactor vessel 3 of the liquid metal reactor by the evaporator section 6 of a thermosyphon 5, and dissipation of the absorbed decay heat to the atmosphere from the condenser section 8 of the thermosyphon 5. The thermosyphon 5 of this invention has a vertical evaporator section 6 that is installed between the concrete wall 2 and a containment vessel 4 as shown in FIG. 1 and surrounds the containment vessel 4 circumferentially at its heat absorption part, an inclined adiabatic section 7 extending upward from the top end of the evaporator section 6, and a vertical condenser section 8 extending upward from the top end of the adiabatic section 7. The condenser section 8 forms the heat dissipation part of the thermosyphon 5.

[0018] The general idea of the thermosyphon or heat pipe and its application for PSDRSs will be described in detail as follows:

[0019] As well known to those skilled in the art, thermosyphons and heat pipes are heat transfer devices making use of a heat transfer cycle, in which vapor naturally flows from an evaporator section having a high vapor pressure to a condenser section having a low vapor pressure due to a difference in the vapor pressure between the evaporator section and the condenser section. In the heat transfer cycle of the thermosyphons or the heat pipes, condensed fluid flows from the condenser section to the evaporator section due to natural force, such as capillary attraction or gravity.

[0020]FIG. 6 is a view, showing the construction and operational theory of a conventional two-phase closed thermosyphon. As shown in the drawing, when the heat absorption part absorbs heat from surroundings, the evaporator section vaporizes the working fluid, thus forming vapor. The vapor flows from the evaporator section to the condenser section through the adiabatic section due to a difference in the vapor pressure between the evaporator section and the condenser section. The vapor is condensed in the condenser section, while latent heat of condensation is dissipated from the heat dissipation part to the surroundings. On the other hand, the condensed fluid flows down from the condenser section along the sidewall of the thermosyphon vessel due to gravity, thus passing through the adiabatic section prior to reaching the evaporator section. When the condensed fluid reaches the evaporation section, one cycle of the working fluid is accomplished.

[0021]FIG. 1 shows the construction of PSDRS using a thermosyphon in accordance with the preferred embodiment of this invention. FIG. 2 shows a heat transfer mechanism of the above PSDRS. As shown in the drawings, the construction of this PSDRS remains the same as that of the conventional PSDRS, except that the PSDRS of this invention has the thermosyphon, different from the conventional PSDRS. FIG. 3 is a plan view of the PSDRS using the thermosyphon of this invention, showing an embodiment of the arrangement of the parts of said PSDRS. As shown in the drawing, numbers of thermosyphon pipes are located around the containment and containment vessel, and each thermosyphon pipe consists of evaporator, adiabatic, and condenser sections. The adiabatic section 7 connects the evaporator section 6 to the condenser section 8. This adiabatic section 9 is covered with an insulator 9 around its sidewall, and so it does not perform any heat exchanging operation with the surroundings, but forms an inclined passage having a proper gradient suitable for allowing a downward flow of liquid-phase working fluid in addition to an upward flow of vapor-phase working fluid. For the condenser section 8, finned pipes are used to enhance heat transfer between the condenser section and the atmosphere.

APPENDIX A: ABBREVIATIONS

[0022] Conv1: first convective heat transfer from the hot sidewall of the containment vessel to air flowing in the hot air passage.

[0023] Conv2: second convective heat transfer from the hot sidewall of the thermosyphon to air flowing in the hot air passage.

[0024] pore: pores formed in a wick.

[0025] Rad: radiant heat transfer from the hot sidewall of the containment vessel to the air separator or the sidewall of the thermosyphon.

APPENDIX B: REFERENCES

[0026] 1. Y. S. Sim et al, Analysis of Decay Heat removal Characteristics of PSDRS, KNS'98 Spring Collection of Academic Essays, pp. 653-659, 1998.

[0027] 2. Y. S. Sim et al, Heat Transfer Enhancement by Structures for an Air Channel of LMR Decay Heat Removal, Nuclear Engineering and Design, 199, pp. 167-186, 2000.

[0028] 3. A. S. Robertson & E. C. Cady, Heat Pipe Dry Cooling for Electrical Generating Stations, Proceedings of the 4^(th) Int. Heat Pipe Conf., Sep. 7-10, 1981, London, UK, pp 745-758.

[0029] 4. P. D. Dunn & D. A. Reay, Heat Pipes, 3^(rd) Edition, Pergamon Press, 1982.

[0030] 5. Y. Lee & U. Mital, A Two-Phase Closed Thermosyphon, Int. J. Heat Mass Transfer, Vol. 15, pp 1695-1707, 1972.

[0031] 6. Y. Lee & A. Bedrossian, The Characteristics of Heat Exchangers Using Heat Pipes or Thermosyphons, Int. J. Heat Mass Transfer, Vol. 21, pp. 221-229, 1978.

[0032] 7. Adrian Bejan, Convection Heat Transfer, John Wiley & Sons, 1984 

What is claimed is:
 1. A method of removing decay heat from a liquid metal reactor using a thermosyphon, comprising the steps of: absorbing the decay heat from said reactor at an evaporator section of the thermosyphon; and dissipating the absorbed heat to the atmosphere from a condenser section of the thermosyphon.
 2. A device for removing decay heat from a liquid metal reactor installed at a position between a containment and a reactor support concrete wall, comprising: a thermosyphon installed at a position between said reactor support concrete wall and a vessel of said containment.
 3. The device according to claim 2, wherein said thermosyphon comprises a vertical evaporator section, an inclined adiabatic section extending upward from a top end of said evaporator section, and a vertical condenser section extending upward from a top end of said adiabatic section. 